The Center for women's reproductive health offers a last chance at hope - but nobody ends up there by choice.

Its very existence is controversial, and to the demonstrators who barricade the building every day, the service it offers is no different from legalised murder.

Now life and death decisions are being made horrifyingly real: a lone protester with a gun has taken the staff, patients and visitors hostage.

Starting at the tensest moment in the negotiations for their release, A Spark of Light unravels backwards, revealing hour by urgent hour what brought each of these people - the gunman, the negotiator, the doctors, nurses and women who have come to them for treatment - to this point.

And certainties unwind as truths and secrets are peeled away, revealing the complexity of balancing the right to life with the right to choose.